In many cases, an electromechanical drive for driving an actuator, e.g. a wheel or a chain track, comprises an electrical power converter, an electrical machine, and a gearbox between the electrical machine and the actuator. The electromechanical drive can be for example a part of an electromechanical power transmission chain which comprises a generator for supplying electrical power to the electrical power converter. The generator can be driven with a combustion engine that can be e.g. a diesel engine, an Otto-cycle engine, or a turbine engine. The electromechanical power transmission chain can be, in turn, a part of for example a working machine that can be a mobile working machine having wheels and/or chain tracks. A mobile working machine can be, for example, a tractor, a bucket charger, a road drag, an excavator, or a bulldozer. It is also possible that the working machine is for example a stone crusher or a wood chipping machine that is not necessarily provided with means for moving the working machine. The electromechanical power transmission chain provides advantages compared to a traditional mechanical power transmission chain because for example the rotational speed of the combustion engine can be more freely selected from the viewpoint of the operational efficiency of the combustion engine, and thus savings in the fuel costs can be achieved.
Typically, the transmission ratio provided by the gearbox of the electromechanical drive is selected manually or by a high level control system. Thereafter, a torque or speed reference of the electrical machine is supplied to the electrical power converter, wherein the torque or speed reference of the electrical machine depends on the prevailing transmission ratio provided by the gear box and on the desired operation of the actuator, e.g. a wheel or a chain track.
The approach of the kind described above is, however, not free from challenges. One the challenges is related to cases where the prevailing transmission ratio provided by the gearbox happens to be such that the operation point of the electrical motor becomes non-optimal from the viewpoint of losses and/or some other factors.